A precalibrated flowmeter will be developed to compute blood flow unambiguously by taking the product of the mean value of flow velocity through a given surface and the areas of that surface. This device will offer a stable calibration factor unaffected by changes in temperature, vessel diameter, or flow velocity profile; a zero-voltage zero-flow base line; and a convenient chronic measurement of volumetric flow under laminar or turbulent conditions. A spherical illumination pattern is obtained by pulsing a single spherical transmitting-receiving crystal. The back-scattered energy from the blood to the crystal is received from that surface in the vessel formed by its intersection with a sphere having a radius determined by the time between the excitation pulse and the closure of gate to the receiving electronics. The mean value of the Doppler shift in the back-scattered energy, obtained by spectrum analysis, is proportional to the mean velocity through the surface. The product of the normal velocity and the area, as determined by the pulse echo technique, equals true volumetric flow. This novel approach of determining flow by measuring normal velocity and a specific area eliminates ambiguities caused by the presence of radial flow components and by changes in flow profile shape; moreover, since the area is measured, errors due to its variation are reduced. When these improvements are allied with the stable zero-flow base line of the Doppler technique, the ensuing accurate measuremet of blood flow in both small and large vessels will eliminate the need to reconfirm the sensitivity factor, establish a zero-flow base line with an occluder, or measure the vessel diameter by an independent means.